Effect of cimetidine on delayed hypersensitivity

Cimetidine-induced augmentation of allergic contact hypersensitivity reactions in mice

BALB/c mice were treated with cimetidine (100 mg/kg) or saline, intraperitoneally, twice daily, from days 0-2 or days 7-9 after sensitization with 0.1%, 2,4,6-trinitro-1-chlorobenzene (TNCB) on day 0. On day 7, the mice were challenged with 1% TNCB to one ear. Ear swelling responses (as an index of sensitization), serum histamine levels, and biopsy specimens of challenged ears were evaluated in groups of cimetidine- or saline-treated mice at 0, 0.5, 1, 1.5, 2, 4, 6, 8, 12, 24, and 48 h after challenge. Additional controls included mice injected with saline or cimetidine and challenged with, but not sensitized to, TNCB (irritant controls). Treatment with cimetidine during the induction but not the elicitation of allergic contact hypersensitivity (ACH) produced a significant enhancement of the response throughout the first 48 h. There was no effect of cimetidine on antigen-presenting cells within the epidermis which might account for this enhancement. Similarly, no difference in mast cell morphology or serum histamine levels between cimetidine- and saline-treated groups was observed. Histologically, the cimetidine-treated animals showed a more intense cellular infiltrate, which was most noticeable at 24 to 48 h, at which time numerous subcorneal and perifollicular neutrophilic abscesses were observed. To further investigate the mechanism of action of cimetidine, mice were injected with cyclophosphamide (150 mg/kg) 2 d prior to sensitization. Mice treated with cyclophosphamide alone or in combination with cimetidine showed no additive or synergistic effect upon the ear swelling response. We conclude that enhancement of ACH by cimetidine is independent of any effect on mast cells or antigen-presenting cells, but may relate to a cimetidine-induced inhibition of the induction of T-suppressor cells at the time of sensitization.

Cimetidine: an immunomodulator

Suppressor T lymphocytes possess histamine2 (H2) receptors and contribute significantly to the function of the immune system. Experimentally, cimetidine, an H2-receptor antagonist, has been shown to enhance a variety of immunologic functions both in vivo and in vitro because of its inhibitory effects on suppressor-cell function. Successful tumor immunotherapy, as well as some protection from infection, has been reported in experimental animals. Patients receiving cimetidine have been shown to exhibit enhanced cell-mediated immunity as evaluated by increased response to skin-test antigens, restoration of sensitivity following development of acquired tolerance, and increased responses of lymphocytes to mitogen stimulation. Preliminary reports also indicate that cimetidine may offer therapeutic benefits for patients with Varicella zoster and Herpes simplex infections, as well as those suffering from mucocutaneous candidiasis and common variable hypogammaglobulinemia. These immunoregulatory effects are dose-related but are not always consistent. Because of its inhibitory effect on suppressor function, cimetidine treatment may be deleterious in patients with organ transplant and autoimmune disorders. Cimetidine should be used as an immunomodulator on an experimental basis only.

"Immunoregulatory effects of cimetidine: inhibition of suppressor cell effector function in vivo"

The effects of cimetidine upon suppressor cell effector function in a well-studied murine model of contact hypersensitivity were examined. Intravenous inoculation of BALB/c mice with DNP-coupled syngeneic spleen cells induced the production of DNP-specific suppressor cells which was demonstrated by a reduction in ear swelling after contact sensitization with 1-fluoro-2, 4-dinitrobenzene (DNFB) following transfer of spleen and lymph node cells to naive syngeneic recipients. Cimetidine treatment of mice who had also received suppressor cells eliminated the manifestation of suppressor cell activity as measured by the development of normal immunologic response following contact sensitization with DNFB. While all the groups receiving cimetidine showed restoration of delayed hypersensitivity, the maximum effect was seen when 50 mg/kg of cimetidine was administered on Day 5 (day of challenge). These results indicate that, in addition to its previously described inhibitory role in suppressor cell induction, cimetidine is also capable of inhibiting suppressor cell effector function. The involvement of histamine in both these processes in vivo is also suggested.

Enhancement of anti-sheep erythrocyte plaque-forming cell levels by cimetidine in vivo

Previous studies demonstrated an immunomodulatory role for cimetidine in contact sensitivity responses in vivo. The present experiments have examined the effects of cimetidine upon in vivo antibody production. When given intravenously, cimetidine treatment consistently resulted in enhanced numbers of IgM plaque-forming cells (PFC) following immunization with sheep erythrocytes. This enhancement was dependent upon both the dose and timing of cimetidine administration. In timing experiments, maximal enhancement of PFC levels was obtained when cimetidine was given at the time of or within three days following immunization. Treatment with cimetidine four days after immunization or one day before assay led to a slight decline in PFC level. In contrast, intraperitoneal treatment with cimetidine has little effect upon the anti-sheep erythrocyte PFC level regardless of dose or timing. Overall, these results indicate that cimetidine may be capable of modulating PFC development in vivo. This modulation, however, depends critically upon dose, timing, and route of cimetidine administration.

The effect of cimetidine on immunological parameters in Crohn's disease: a double blind trial

Thirty-six patients with Crohn's disease were entered into a double-blind trial to assess any beneficial effect that cimetidine might have on immunological and clinical status. Eighteen patients were randomized to receive cimetidine, 1 g orally for 28 days, and the other 18 patients to receive a placebo. There was no alteration in clinical status in the cimetidine-treated group. Although 64% of the patients were anergic, augmentation of skin tests to candida, mumps, tuberculin, streptokinase/streptodornase and trichophyton antigens, was not observed in the cimetidine-treated patients. The patients with Crohn's disease, as a whole had higher absolute numbers of suppressor T-lymphocytes, 0.70 X 10(9)/litre (0.21-2.36, n = 35) compared to control values, 0.5 X 10(9)/litre (0.16-1.55, n = 25) (P less than 0.05). However, there was no significant difference in proportions of suppressor and helper T-lymphocytes, lymphocyte activation and humoral immunity after cimetidine treatment. The lack of any clear modulation of immunity by cimetidine, would be against trying H2 antagonists in a long term clinical trial.